1. Field of the Invention
The present invention relates to a magnetic recording medium, more specifically, a magnetic recording medium having excellent friction and sliding properties and used in a contact-start-stop (CSS) system, and to a magnetic disc device using the same.
2. Description of the Related Art
In recent years, as the amount of the information processed in computer systems increases, the information to be recorded in a magnetic disc device has increased so that the device must have a more compact size and larger capacity and, also, the device is required to have a higher recording density. To cope with this tendency, efforts have been made to improve the device as a whole, such as a magnetic head, a magnetic recording medium, a head positioning mechanism and a signal processing circuit.
In a current disc device, a CSS (contact-start-stop) system (in which a magnetic head is in contact with a medium when the device is off, and the magnetic head flies above the disc surface when the disc rotates) surface when the disc rotates, is used. In this system, if the surface roughness and the lubricant film thickness of the medium are not appropriate, a head adsorption phenomenon, where a head and a medium are bonded to each other, is brought about when the disc device is off.
Accordingly, it is important for the medium to have an appropriate surface roughness. At present, the surface is mechanically roughened using a lapping tape or free abrasives.
To achieve a higher density, one important factor to increase the recording density is to decrease the distance between the magnetic head and the medium, i.e., the head floating height. A low floating height of the magnetic head causes an increase in the probability of a collision between a magnetic head and a magnetic recording medium and eventually a head crash wherein recorded information is lost. To avoid this, the surface roughness of a medium has been rendered low. However, in the current circumstances, where the head floating height is reduced to as low as about 0.1 .mu.m, a fine and uniform roughness over the entire surface of the medium cannot be obtained by a mechanical surface roughening method.
Thus, methods for attaining a surface roughness of the medium by means other than mechanical means have been proposed in, for example, Japanese Unexamined Patent Publication (Kokai) Nos. 3-73419 and 2-137120. In Japanese Unexamined Patent Publication (Kokai) No. 3-73419, a roughness is provided on the medium surface by forming a film of a low melting point metal in the form of islands on the surface of a substrate. In Japanese Unexamined Patent Publication (Kokai) No. 2-137120, a surface roughness of the medium is provided by forming a protective film containing fine particles.
However, in the case of Japanese Unexamined Patent Publication (Kokai) No. 3-73419, the size and density of islands in the film largely depend on the temperature and the surface condition of the substrate at the time of forming the film. Depending upon the kind of substrate, an upper limit of the allowable temperature of the substrate exists and a desired film in the form of islands may not be obtained. Further, although the difference in the surface condition may be eliminated by forming an island film after forming an undercoat film on a substrate, the application of the undercoat film causes an increase in cost by requiring an additional device or target. On the other hand, in the case of Japanese Unexamined Patent Publication (Kokai) No. 2-137120, fine particles may be removed from the protective layer due to the sliding of the head and may enter between the head and the medium, which may give rise to a head crash. In addition, the smaller the size of the fine particles, the more difficult the production thereof and the worse the dispersibility. The difficulty in making the particles smaller throws the effort for achieving a lower flying height into difficulties.